Field of the Invention
The present invention relates to a synchronous motor control device for use in an electric motor for traction in an electric vehicle in which a running drive source is only the electric motor or a hybrid type electric vehicle equipped with the electric motor and an engine.
Description of Related Art
In electric vehicles, synchronous motors which are AC-driven permanent magnet motors such as an IPM (Inter Permanent Magnet) motor and an SPM (Surface Permanent Magnet) motor are often used as traction motors. These synchronous motors for the electric vehicle are driven by a vector control type inverter device in order to enhance the control performance thereof, but torque ripple generated due to the structure of the motor including a permanent magnet has a frequency which is six times that of a power supply frequency which occurs due to harmonic of field magnetic flux.
Giving a description with reference to FIG. 1B, motor torque Te outputted in response to a target current value Iref supplied to a motor 2 includes torque ripple as schematically shown as a torque waveform.
If torque ripple occurs in the motor as described above, in the case of an electric vehicle, the torque ripple leads directly to vibrations of a vehicle body, which deteriorates the ride comfort.
As a technique to reduce torque ripple, it has been proposed to perform compensation of cancelling out torque ripple of IPM motor output, specifically, to add d-axis, q-axis current commands or a torque command according to a vector control theoretical model formula for the IPM motor (e.g., Patent Document 1).